In recent years, a Group III nitride compound semiconductor has been receiving attention as a semiconductor material for light emitting devices that emit short-wavelength light. In general, with various types of crystalline oxides, silicon carbide, single crystals, Group III-V compound semiconductor single crystals, or the like, such as sapphire single crystals, serving as a substrate, a Group III nitride compound semiconductor is laminated and formed thereon by means of a metal organic chemical vapor deposition method (MOCVD method), a molecular beam epitaxy method (MBE method), or a hydride vapor phase epitaxy method (HVPE method).
The crystal growth method widely used at present is a method wherein sapphire, SiC, GaN, AlN, or the like is used as a substrate, and fabrication is performed thereon by means of a metal organic chemical vapor deposition method (MOCVD method), in which a Group III organic metallic compound and a group-V material gas are used in a reaction tube having the above substrate installed therein, to thereby grow an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, in a temperature region of 700° C. to 1200° C.
After the respective semiconductor layers have been grown, a negative electrode is formed on the substrate or on the n-type semiconductor layer, and a positive electrode is formed on the p-type semiconductor layer, to thereby obtain a light emitting device.
A conventional active layer employs: a double hetero structure in which InGaN, the composition of which has been adjusted for adjusting light emission wavelength, is used and this active layer is sandwiched by layers with a bandgap higher than that of InGaN; or a multiple quantum well structure in which the quantum well effect is used (for example, refer to Patent Documents 1 to 4).
Moreover, the p-type semiconductor layer is generally constituted by: a p-type clad layer that has a bandgap greater than that of the active layer and that has a functionality to block, with a potential barrier based on the gap difference therebetween, electrons and holes; and a p-type contact layer to which a p-type electrode is to be joined.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. H10-79501
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. H11-354839
[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2001-68733